Sorbitol is a hexitol principally used in the fields of food industry and pharmaceutical applications as an artificial sweetener, but also for its reduced calorie content and acariogenicity.
Sorbitol, like other polyols such as xylitol or mannitol, is commonly used as a pharmaceutical excipient, as a sweetener and texturizer in the food industry, and as an additive medium in all types of industries. However it is a better excipient than xylitol and mannitol, in particular under compression, as a result of its particular ability to crystallize in the form of directly compressible needle crystals.
Generally, in order to have available a crystallized sorbitol with high compression resistance, it is necessary to produce a γ crystalline form of sorbitol (α- and β-forms are particularly unstable) by working with a supersaturated sorbitol solution, in which the γ form represents at least 90%.
However, even when it is crystallized in this more stable γ form, the granulated sorbitol obtained in a standard fashion has a certain number of drawbacks, including that of being very hygroscopic.
This high hygroscopicity results in the flow of the granulated sorbitol becoming difficult, even impossible, whenever water uptake has occurred.
In order to avoid this problem of the flow of granulated sorbitol, it was recommended in patent FR 1,506,334 to prepare a low-density sorbitol with a higher particle size (comprised between 0.42 and 1.19 mm).
However, it has been established that as the bulk density of a granulated sorbitol decreases, the more friable it becomes, i.e. affected by an alteration in its particle size by mechanical action. Moreover, the dissolution times of this granulated product with a coarse particle size are generally too long and therefore unsuitable.
Finally, although the flow properties are partially improved by using particles of such a particle size, the residual hygroscopic character which is still too high militates against the use of this granulated sorbitol in all cases where it is combined with ingredients or additives which are highly affected by water.
It is also established that the ability to fix large quantities of additives is a direct function of the specific surface area of said particles.
The absorption capacities of the granulated sorbitol are thus greater as its specific surface area increases. However, it is known that the specific surface area of the dense crystals of commercial γ sorbitol is very low.
Thus, for a particle size comprised between 500 and 1000 μm, it is equal to 0.7 m2/g at most.
With the aim of preparing a dry sorbitol having a better particle size, good flow properties and satisfying the desired conditions of compressibility, patent application FR 2,622,190 describes a sorbitol powder containing particles having a relatively high average diameter comprised between 350 and 500 μm.
However, the high bulk density and the low specific surface area, of the order of 0.9 a 1.2 m2/g, are not significantly modified by the spray manufacturing process used, such that the sorbitol thus obtained retains the same moisture adsorption factor and the same solubility in water as the starting sorbitol powder.
Patent EP 32,288 describes a polymorph of sorbitol having a disrupted and loosely-packed crystalline structure, presenting an improved hygroscopicity and satisfactory compression properties. However, these particular properties only relate to a particle size fraction comprised between 250 and 841 μm (i.e. 60/20 mesh), the specific surface area of which is in any case less than 2 m2/g.
Patent EP 380,219 describes free-flowing polymorphic forms of sorbitol having a specific surface area which can reach 5 m2/g, the apparent density of which is high (up to 0.7 g/ml) and the solubility rate in water satisfactory.
However, in order to achieve this result, it is necessary to prepare, by spraying open-centred spherules of acicular microcrystals of thickness less than 1 μm and length comprised between 5 and 20 μm.
Moreover, it is recommended in this patent to use sorbitol/mannitol mixtures or to add saccharose.
It can be seen from all of the above that there is an unmet need for a granulated sorbitol having a specific surface area and a compressibility as high as possible, while maintaining a satisfactory particle size, density and free flow.
Thus by devising and preparing a new granulated sorbitol at the cost of much research, the Applicant has creditably reconciled all these aims hitherto regarded as irreconcilable.